1. Field of the Invention
The present invention relates generally to magnetic information storage and retrieval, more particularly to magnetic tape storage devices and components, and specifically to a tape guide for magnetic tape as exemplified for use in a computer backup tape transport subsystem.
2. Description of the Related Art
Despite the advent and popularity of magnetic tape cartridges having an integral tape supply connected to both supply and a take-up reels, applications remain in which loose-ended, 1/2-inch wide, magnetic tape is used. Such magnetic tape finds applications in both the audio recording and computer industries, such as in a data cartridge form as defined by American National Standard (ANSI) X3.180-1990. More specifically, this cartridge has a single supply reel of magnetic tape that has a tape leader block attached to the free end of the tape. The tape is loaded from the cartridge to a take-up hub in the tape transport system (interchangeably referred to as a "drive") by extracting the leader block and threading the tape passed a read/write transducer (the transducer subassembly is also referred to as a "head"). The Cipher Data Products, Inc. model 3000i drive and TapeXpress drive ("TapeXpress" and the "3000i" logo are trademarks of Cipher Data Products) and the IBM model 3480 tape drive ("IBM" is a registered trademark of International Business Machines Company) utilize this cartridge.
Drives designed specifically for a such a tape cartridge are described in U.S. Pat. Nos. 4,704,645, 4,809,099 and 4,852,825 to the common assignee of the present invention, incorporated herein by reference.
As shown in FIG. 1 (Prior Art), it is known to thread magnetic tape 2 passed a magnetic head 4 that includes at least one read/write transducer subsystem. In the tape path, tape guides 6, 8 are mounted on a deck plate 9 that is typically part of the frame of the drive. These guides 6, 8 are appropriately positioned with respect to the head 4 in order to assure a proper attack angle and alignment of the tape 2 with read/write gaps 10, 12 in the head 4. To improve alignment between the tape and head and tape travel stability over the head 4, more guides (not shown) are often added between the supply and take-up reels.
The tape 2 in such a drive is used, for example by IBM, specifically to write eighteen tracks in parallel. The head 4 has one common write gap line and one common read gap line with eighteen individual read or write coils per track. Other transports using this same cartridge, such as the 3000i drive, have been designed to record up to twenty-four parallel tracks recorded in a serpentine fashion (also known as "streamer" tape drives), using a single head that is stepped to an addressed track. Track position is determined by the tape guides while track width is controlled by the core dimensions of the head. Since it is known to have the track width between 0.017 and 0.021 inch in such drives, it is of extreme importance that the tape be consistently guided passed the read/write gaps 10, 12 in head 4. Accurate alignment is critical to repeatable read/write functionality.
In the prior art, it is known to use a static, non-rotating guide mechanism 6 as a tape guide bearing, having ceramic flange members 14, 16 on the top and bottom of a guide 18 against which the tape 2 is drawn by motors coupled to supply and take-up reels (not shown). [It will be recognized by a person skilled in the art that a tape drive may be installed internally to a computer, rack mounted, or be a freestanding computer peripheral. Hence, while the common terms "top" and "bottom" are used herein for convenience of explanation and clarity, it should be understood that such terms are not to be construed as limitations; for example, a freestanding computer peripheral could be used in a stand which actually operates the drive while standing on its edge.] These full flanges 14, 16, or ceramic tipped springs, are used to provide an edge force on the upper edge 26 of the magnetic tape 2 in order to position the tape against a reference surface with respect to the head gaps 10, 12. In some such devices, air pressure, applied by an internal compressor or pump, is used with this type of static guide mechanism 6 to minimize tape frictional drag and to prevent the type from sticking to the generally smooth surface of the guide 18.
Also shown in FIG. 1, another method known in the art uses a conical spring 20 on top of a ceramic flange member 14' that covers the top of a static or roller-type barrel 22 in order to provide an appropriate edge force to the edge of tape 2. However, it has been found that this type of spring 20 generally provides an unbalanced force to the tape 2. Too high a pressure can damage the tape and too low a pressure allows the tape to wander across the face of the head, misaligning tracks with respect to the read/write gaps 10, 12. Additionally, stiction can still occur between the abutting, recorded surface of the tape 2 and roller barrel 32 unless an air bearing system is again used.
The expensive, ceramic flanges 14, 14' used to "squeeze" the tape 2 have also been found to turn during tape motion if mounted on a circular rod or to bind on a non-circular mounting post 18 or roller 22. This effect can damage also the tape 2.
Moreover, operative parts of the nature of the prior art are generally comparatively large when compared to the new, smaller tape paths such as may be found in use with a desktop, personal computer where the tape drive may have to be configured to fit into the same form factor as a floppy disk drive.
Thus, there is a need for an improved, inexpensive tape guide device for use in threaded magnetic tape transport systems.